In telecommunications, collocation is a physical arrangement in which two objects are placed close together. Collocation may occur between two pieces of radio equipment, for example. On a collocated multiple-radio platform, adjacent or alternate channel interference among heterogeneous radio devices has become an issue of concern. A transmitted signal from one radio may leak into a collocated radio and cause degradation in the performance of its receiver. The object in which degradation occurs is known herein as the victim, e.g., victim radio, victim transmitter, or victim receiver. The typical co-existence transmitter-to-receiver interference scenarios are transmitter noise at the channel frequency of the receiver and receiver blocking by the collocated transmitter.
Transmitter noise is due to out-of-band (OOB) emission from imperfect filtering or phase/LO (local oscillator) noise in the transmitter. Transmitter noise may take the form of colored noise, white noise or spurs. Receiver blocking is due to several mechanisms, such as compression of the receiver, cross modulation between the receiver and the transmitter's leakage signal, limited dynamic range of an analog-to-digital (A/D) converter in the receiver, reciprocal mixing, and so on.
Clock signals are typically characterized as digital square wave pulses, with sharp edges that contain significant spectral energy. The spectral energy produces harmonic frequency components, hereinafter called harmonics, at frequencies that are integer multiples of the frequency of the clock signal. The harmonics may radiate from lines carrying the clock signal, which interconnect the logic circuitry. The harmonics may inter-modulate with one radio's transmission signals, to generate interference in the other radio's frequency band.